> Is some work being done on a debugger for the Mac/Windows OCaml versions ?

None that I know of.  The debugger from the Unix version relies
heavily on two Unix-specific features: Unix-domain sockets and the
fork() system call (used as a cheap and surprisingly efficient
checkpointing mechanism for the replay facility).  Under Windows at
least, a replacement for Unix-domain sockets could be found, but I
wasn't able to find an adequate checkpointing mechanism.

- Xavier Leroy